This invention relates to aerosol dispersions that are highly stable and are useful for treating a variety of surfaces. In particular, it relates to biliquid foam dispersions in aerosol form.
A wide variety of emulsions have been aerosolized by mixing them with gas propellants in an aerosol container. See generally U.S. Pat. Nos. 3,669,892, 4,354,871, 4,880,557, 5,753,607. These emulsions can deliver furniture polishes, cleaning compounds, insecticidal or insect repellant compounds, herbicidal materials, cosmetic materials, or other desired surface treatment materials.
Common problems encountered in creating such emulsions are that surfactants are necessary for the emulsification, and as the level of surfactant decreases the stability of the emulsion often correspondingly decreases. This can result in either a need to shake the product before use (to obtain the desired mixture), or where surfactant levels are higher side effects due to the presence of high levels of surfactant (e.g. unwanted residues on the surface contacted; skin irritation;                adverse effects on other chemistry such as certain antimicrobial compounds).        
Also, in certain emulsions particularly desirable additives (e.g. silicone oils in furniture polish) tend to lead to stability and/or solubility problems unless polar hydrocarbon solvents are also used. Some polar hydrocarbon solvents (especially alcohols) can be undesirable in certain contexts due to environmental or flammability concerns.
As disclosed in U.S. Pat. No. 3,965,518, when desired actives (e.g. furniture polish materials or fragrances) are delivered via an aerosol, an aerosol can may be charged with emulsified active and a propellant. The propellant is typically a hydrocarbon gas such as butane, propane, isobutane, isopropane, or mixtures thereof, or sometimes carbon dioxide. The active is sprayed from the can onto the surface to be treated. Substantial amounts of propellant (e.g. ten percent by weight) are typically added, thereby altering the stability and/or uniformity characteristics of the emulsion.
In unrelated work the art has developed oil-in-water non-aerosol dispersions known as biliquid foams. In these dispersions the oil is present in discrete droplets surrounded by a first surfactant. The remaining water has dissolved in it a second surfactant. The second surfactant migrates to the surfactant-coated surface of the oil to create at least some drops (preferably most oil drops) surrounded by a bilayer of surfactant. See generally U.S. Pat. Nos. 4,486,333 and 6,312,760. See also F. Sebba, Biliquid Foams-A Preliminary Report, 40 J. Colloid. Interface Sci. 468-474 (1972); O. Sonneville-Aubrun et al., Surfactant Films In Biliquid Foams, 16 Langmuir 1566-1579 (2000) and a Disperse Technologies Limited 1998 technical presentation entitled “Advanced Topical Dispersion Technology”.
Early versions of these foams suffered from significant instability. However, U.S. Pat. No. 6,165,479 taught that adding a viscosity modifier/thickener to such foams would markedly increase the stability of the foam. However, this patent was focused on formulating cosmetics, and thus did not address design/formulation problems in creating aerosolized biliquid foams.
In this regard, if a designer had considered rendering a non-aerosolized biliquid foam into an aerosolized form, there would have been the concern regarding clogging and non-uniform spray that one would have expected thickening agents to cause. Further, one would have expected that adding a propellant in such high quantity to a biliquid foam dispersion might cause instability concerns and/or uniformity concerns.
Thus, a need still exists for improved aerosolized dispersions, particularly those that are stable over the long term.